Temperature and host dependence of the transition interference between f–f and f–d transitions of Sm²⁺ in matlockites

The absorption spectra of Sm²⁺ doped in MFX (M=Sr, Ba; X=Cl, Br) crystals were studied within the range of 20,000–35,000 cm⁻¹ as a function of temperature and host. The absorption bands observed were described with a simple model developed by Wood and Kaiser using group theory. The temperature and host dependence on the ⁷F₀→⁵D₃ Fano resonance lines were investigated. BaFCl:Sm²⁺ system showed a "normal" ⁷F₀→⁵D₃ transition at 4 K in spite of similar crystal structure and absorption profile with other MFX hosts. New Fano resonances were observed in the absorption spectra at higher energies (23,000–25,000 cm⁻¹) for all MFX:Sm²⁺ systems at 4 K which persist up to room temperature. Preliminary energy level calculation showed that these resonance lines involve the interaction between higher excited ⁵L_J states of 4f⁶ configuration and 4f⁵5d¹ configuration. - Highlights: • The absorption spectra of Sm²⁺ doped in MFX (M=Sr, Ba; X=Cl, Br) crystals within the range of as a function of temperature and host. • The absorption bands described with a simple model developed by Wood and Kaiser using group theory. • BaFCl:Sm²⁺ system showed a "normal" ⁷F₀→⁵D₃ transition at 4 K in spite of similar crystal structure and absorption profile with other MFX hosts. • New Fano resonances observed in the absorption spectra at higher energies (23,000–25,000 cm⁻¹) for all MFX:Sm²⁺ systems at 4 K which persist up to room temperature